To date, an image sensor using a charge-coupled device has been widely utilized in photographic apparatuses, such as digital cameras. Some photographic subjects, however, have contrasts exceeding the dynamic range of the image sensor. For example, a photographic subject may include an object exposed to sunlight (hereinafter referred to as a “bright object” for the sake of convenience) and an object placed in the shade (hereinafter referred to as a “dark object” for the sake of convenience). In such a case, if the exposure amount of a photographic apparatus is adjusted so as to make a dark object visible in an image, the luminance of a bright object exceeds the upper limit of the dynamic range of the image sensor, and, as a result, the bright object is shown as a solid white object in the image. In contrast, if the exposure amount of the photographic apparatus is adjusted so as to make a bright object visible in an image, the luminance of a dark object is lower than the lower limit of the dynamic range of the image sensor, and, as a result, the dark object is shown as a solid black object in the image.
To address this, a technology that combines a plurality of images obtained by photographing a subject with different amounts of exposure to virtually extend the dynamic range of an image sensor has been proposed (see Japanese Laid-open Patent Publication No. 2004-254151, for example). Such a technology is referred to as high dynamic range (HDR) imaging.
For example, Japanese Laid-open Patent Publication No. 2004-254151 discloses an imaging device that combines a first image signal obtained by photographing with a large amount of exposure and a second image signal obtained by photographing with a small amount of exposure. The imaging device uses a second image signal for a region of a moving photographic subject and a saturation region of the first image signal, for example. Regarding other regions, the imaging device varies the proportions accounted for by the first image and the second image, for example, in such a manner that, with increasing proximity to the saturation level of the first image signal, the larger the proportion accounted for by the second image signal. Under such a condition, the imaging device performs image combining.